Power supply systems such as these are generally known. Reference is made, purely by way of example, to EP 0 847 612 B1 and to EP 0 023 058 A1.
Polyphase arc furnaces represent a highly nonlinear load. The nonlinearities result in considerable reactions on the power supply system, in particular so-called flicker. For this reason, power supply systems for polyphase arc furnaces generally have a power factor corrector. The power factor corrector is connected in parallel with the furnace transformer. In the simplest case, the power factor corrector may be in the form, for example, of a so-called TCR (thyristor controlled reactor), see the cited EP 0 847 612 B1. It is likewise known for the power factor corrector to be in the form of a STATCOM (static compensator). In this context, reference is made, purely by way of example, to U.S. Pat. No. 6,075,350 A.
The current for operating a polyphase arc furnace is very high. For this reason, attempts are made to arrange the furnace transformer as close as possible to the polyphase arc furnace itself in order that the cable length from the furnace transformer to the polyphase arc furnace can be kept as short as possible. In general, the furnace transformer and the components arranged downstream from the furnace transformer are arranged in the furnace building. The space conditions in the furnace building are quite confined, for this reason. Furthermore, the number of phases and the operating frequency of the polyphase arc furnace in the prior art necessarily matches the number of phases and the operating frequency of the polyphase mains system.
DE 199 20 049 C2 discloses a power supply system for a polyphase arc furnace, in which an indirect converter is arranged immediately upstream of the polyphase arc furnace. The indirect converter has a rectifier on the input side, an inverter on the output side, and a link circuit between them. DE 199 20 049 C2 does not mention a furnace transformer. This may be a component of a polyphase source mentioned in DE 199 20 049 C2.
EP 0 023 058 A1 discloses a power supply system for a polyphase arc furnace, in which control means or converters with thyristors can be provided on the primary and secondary sides of a transformer. The control means and converters are in the form of current controllers, according to EP 0 023 058 A1.
DE 30 25 644 A1 discloses a power supply system for a polyphase arc furnace, in which the primary of a furnace transformer is connected directly to the polyphase mains system, and the secondary is connected directly to the polyphase arc furnace. The phases on the output side of the furnace transformer are connected to one another via bridge circuits, with the bridge circuits each consisting of a capacitor and a switch connected in series.